Cathode material, interconnector material and solid oxide fuel cell

ABSTRACT

A cathode material for a solid oxide fuel cell comprising a complex oxide having a perovskite structure expressed by the general formula ABO 3  with a standard deviation value of no more than 10.3 for the atomic percentage of respective elements in the A site measured using energy dispersive X-ray spectroscopy at 10 spots in a single field.

BACKGROUND

1. Technical Field

The present invention relates to a cathode material, an interconnectormaterial, and a solid oxide fuel cell.

2. Description of the Related Art

In recent years, several materials and structures have been proposed inrelation to fuel cell batteries due to the attention focused on fuelcell batteries in light of effective use of energy resources andenvironmental problems.

Patent Literature 1 (JPA-2006-32132) discloses the use of an LSCF powderas a raw material powder for the cathode of a solid oxide fuel cell(SOFC).

SUMMARY

However, the available voltage may be reduced during repeated powergeneration using the fuel cell. The present inventors gained the newinsight that one cause of this reduction in output is deterioration ofthe cathode.

The technique disclosed herein is based on this new insight andaddresses the problem of providing a new cathode material andinterconnector material (generally termed as appropriate below“electrode material”), and a solid oxide fuel cell that includes thesame.

The present inventors conducted diligent research into solving the aboveproblem and as a result gained the insight that the deterioration of acathode and an interconnector (generally referred to below for the sakeof convenience as an “electrode”) can be suppressed by increasing theuniformity of the concentration of the electrode material components.

In that context, a complex oxide having a perovskite structure expressedby the general formula ABO₃ with a standard deviation value of no morethan 10.3 for the atomic percentage of respective elements in the A sitemeasured using energy dispersive X-ray spectroscopy at 10 spots in asingle field.

The solid oxide fuel cell disclosed herein includes a cathode configuredfrom a cathode material according to a first aspect, an anode, and asolid electrolyte layer that is disposed between the anode and thecathode.

The electrode material described above is suitable as a material forforming the electrode of a fuel cell. The electrode formed by thiselectrode material exhibits superior durability while suppressingdeterioration.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a flowchart describing a method of manufacturing an electrodematerial using a solid-phase method;

FIG. 2 is a flowchart describing a method of manufacturing an electrodematerial using a liquid-phase method;

FIG. 3 is a sectional view illustrating the principal features ofconfiguration of a vertically-striped fuel cell;

FIG. 4 is a SEM image of a single field and an image of concentrationmapping in relation to a sample No. 1 according to the example;

FIG. 5 is a SEM image of a single field and an image of concentrationmapping in relation to a sample No. 7 according to the examples;

FIG. 6 is a perspective view illustrating the external appearance of asegmented-in-series fuel cell; and

FIG. 7 is a sectional view along the direction I-I of the arrow in FIG.6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Selected embodiments will now be explained with reference to thedrawings. It will be apparent to those skilled in the art from thisdisclosure that the following descriptions of the embodiments areprovided for illustration only and not for the purpose of limiting theinvention as defined by the appended claims and their equivalents.

1. Electrode Material

The electrode material includes a complex oxide having a perovskitestructure. The electrode material may include components other than acomplex oxide. As described below, the electrode material according tothe present embodiment is suitably used as a material to configure thecathode or the interconnector of the solid oxide fuel cell.

The composition of the complex oxide is expressed by the general formulaABO₃. Furthermore, at least one of La and Sr may be contained in the Asite. An actual example of this type of complex oxide for use as acathode material includes LSCF, that is to say, (La, Sr)(Co, Fe)O₃, LSFthat is to say, (La, Sr)FeO₃, LSC that is to say, (La, Sr)CoO₃, LNF thatis to say, La(Ni, Fe)O₃, SSC that is to say, (Sm, Sr)CoO₃, and the like.These complex oxides are materials that combine characteristics relatedto oxygen ion conductivity and electron conductivity, and are termedmixed conducting materials. Furthermore, examples of an interconnectormaterial include LCC, that is to say, materials such as (La, Ca)CrO₃,and the like.

The electrode material may include the complex oxide as a “principalcomponent”. The feature “include as a principal component” when acomposition X contains a material Y means that the material Y comprisespreferably at least 60 wt % overall of composition X, more preferably 70wt %, and still more preferably at least 90 wt % of the overallcomposition X.

Furthermore, the electrode material may be configured as a powder (forexample, with an average particle diameter of about 1 micrometer to 5micrometers) or a disintegrated product (for example, with an averageparticle diameter of about 5 micrometers to 500 micrometers), or may bea agglomerate that is larger than the disintegrated product.

The electrode material preferably includes a highly uniform compositiondistribution. More specifically, a value of the standard deviation forthe atomic percentage of respective elements contained at the A site areacquired by use of energy dispersive X-ray spectroscopy (EDS) at 10spots in an arbitrary field in the electrode material is preferably nomore than 10.3.

For example, it is assumed that n types of elements A1, A2, A3, . . . Anare contained at the A site. When the value of the standard deviationfor the atomic percentage of the respective elements is acquired withreference to the atomic percentage obtained at 10 spots, if the value ofthe standard deviation for the atomic percentage for the element A1 islarger than the respective values for the standard deviation of theelements A2-An, it is preferred that the value of the standard deviationof the element A1 is no more than 10.3.

The arbitrary field as used herein is suitably within a range observedby an electron microscope such as an electron probe micro analyzer(EPMA) or a scanning electron microscope (SEM), or the like with amagnification of 100 times to 5000 times. The analysis spot size of therespective 10 spots may be no more than 1 micrometer. When thedistribution of the atomic percentage as described below is evaluatedbased on an observation at an excessively small magnification of lessthan 100 times, there are difficulties associated with the determinationof the uniformity of the distribution of each element in the micro rangethat is the object of the present invention. On the other hand, when thedistribution of the atomic percentage is evaluated based on anobservation at an excessively large magnification that exceeds 5000times, there is an increased possibility that only a non-uniform regionor only a uniform region will be observed as a result of the narrowobservation range. As a result, as stated above, it is preferred thatthe magnification of the electron microscope is in the range of 100times to 5000 times.

The position of the 10 spots may be selected for example on the basis ofthe concentration level in 10 stages that are determined in response tothe distribution of the atomic percentages measured using an electronprobe micro analyzer (EPMA). The concentration level in the 10 stages ispreferably set with reference to substantially the entire range of thedistribution of the atomic percentages. For example, the concentrationlevel in the 10 stages can be set by creating 10 divisions in theinterval between the maximum value and the minimum value in thecharacteristic X-ray intensity in the arbitrary field.

2. Method of Manufacturing Electrode Material

An example of a method of manufacturing the electrode material describedin “Section 1.” above will be described below.

More specifically, the method of manufacture includes acquisition of acomplex oxide compound having a perovskite structure.

The method of obtaining the complex oxide compound includes a solidphase method, a liquid phase method (citrate process, Pechini method,co-precipitation method) or the like.

A “solid phase method” refers to a method in which a mixture obtained bymixing a starting material (powder) including constituent elements at apredetermined ratio is fired, and then subjected to comminution toobtain the target material.

A “liquid phase method” is a method for obtaining a target material thatincludes the steps of dissolving a starting material includingconstituent elements into a solution, obtaining a precursor of thetarget material from the solution by precipitation or the like, and thenperforming drying, firing and comminution.

The sequence of steps will be described below making reference to thefigures in relation to a configuration in which the electrode materialis manufactured using a solid phase method, and a configuration in whichthe electrode material is manufactured using a liquid phase method.

2-1 Method of Manufacturing Electrode Materials using Solid Phase Method

FIG. 1 is a flowchart describing a method of manufacturing an electrodematerial using a solid phase method.

Firstly, in a step S101, a starting material is prepared according tothe type of complex oxide. When manufacturing LSCF as a complex oxide,for example, La₂O₃, SrCO₃, Co₃O₄ and Fe₂O₃ are prepared. The averageparticle diameter of La₂O₃ may be 0.1 micrometer to 0.7 micrometer, theaverage particle diameter of SrCO₃ may be 0.1 micrometer to 0.5micrometer, the average particle diameter of Co₃O₄ may be 0.1 micrometerto 1.0 micrometer, and the average particle diameter of Fe₂O₃ may be 0.1micrometer to 0.8 micrometer. Furthermore, it is preferred that theparticle size distribution of the starting material is controlled. Morespecifically, it is desirable that coarse particles of greater than orequal to 20 micrometers are removed in advance by use of an airclassifier or the like. The removal of coarse particles is effective foruniformity when executing mixing and synthesizing in subsequent steps.

Next, in step S102, the starting materials are classified. Morespecifically, for example, the specific surface area of each startingmaterial is adjusted by classification using an air classifier orexample. When manufacturing LSCF as a complex oxide, the specificsurface area of La₂O₃ is adjusted to 1 m²/g to 5 m²/g, the specificsurface area of SrCO₃ is adjusted to 1 m²/g to 7 m²/g, the specificsurface area of Co₃O₄ is adjusted to 1 m²/g to 7 m²/g, and the specificsurface area of Fe₂O₃ is adjusted to 1 m²/g to 10 m²/g.

Next, in a step S103, the respective starting materials are mixed at apredetermined mixing ratio. In the present embodiment, the mixingprocess preferably includes the steps of weighing the respectivestarting materials at a predetermined mixing ratio and placing thematerials into a pot mill together with pebbles (for example,application is possible of the pebbles used in the manufacture ofzirconia or alumina), rotating the pot mill for a predetermined time (10hrs to 120 hrs) in a dry state and then introducing a predeterminedamount (weight ratio relative to the starting material of 50% to 200%)of solvent (for example, when using an aqueous solvent, ion-exchangedwater may be used, and when using a solvent-based material, acetone maybe used), and rotating the pot mill further for a predetermined time (10hr to 300 hr) in a wet state. When performing a uniform mixture ofrespective starting material powders using wet mixing, it is preferredto perform sufficient disintegration under suitable mixing conditions ofthe starting material powder using dry mixing. The pebbles preferablyhave a diameter of 0.5 mm to 5 mm, and are preferably adjusted to 0.5 to3 times the weight of the starting material powder.

In this mixing process, it is preferred to add a predetermined additiveto the respective starting materials. The additives are phosphorus (P),chrome (Cr), and boron (B). The added amount of P is preferably at least1 ppm to no more than 50 ppm in a weight ratio relative to the startingmaterials, and more preferably at least 1 ppm and no more than 30 ppm.The added amount of Cr is preferably at least 1 ppm to no more than 500ppm in a weight ratio relative to the starting materials, and morepreferably at least 1 ppm and no more than 100 ppm. The added amount ofB is preferably at least 1 ppm to no more than 50 ppm in a weight ratiorelative to the starting materials, and more preferably at least 1 ppmand no more than 10 ppm. The additives are preferably added as oxides.The additives have the function of creating a uniform dispersion andmixture in the constituent components. In addition to comminution of thestarting materials in a dry mix in the previous step, an importantfactor in the control (uniformity) of the composition distribution ofthe electrode material is the combination of a process of wet mixing inlater steps. The mixing ratio of each starting material whenmanufacturing LSCF as a complex oxide may be performed by adjusting thestarting material ratio of La₂O₃, SrCO₃, Co₃O₄ and Fe₂O₃ in accordancewith the composition of the complex oxide.

Next, in step S104, the electrode material is synthesized by firing ofthe starting materials mixed in the pot mill. The synthesis conditionsmay be suitably adjusted within a range of a synthesis temperature of900 degrees C. to 1400 degrees C. and a synthesis time of 1 to 30 hrs inan oxidizing atmosphere.

Next, in step S105, the electrode material in a synthesized agglomeratedconfiguration is subjected to comminution. More specifically, theaverage particle diameter of the electrode material is adjusted to 0.3micrometers to 1.2 micrometers by introducing the electrode materialwith pebbles (for example, application is possible of the pebbles usedin the manufacture of zirconia or alumina) into the pot mill androtating for a predetermined time (5 hrs to 20 hrs). Furthermore, priorto comminution, the electrode material in an agglomerated configurationmay be subjected to preparatory disintegration.

Next, in step S106, the electrode material after comminution isclassified. More specifically, the specific surface area of eachstarting material is adjusted by classification using an air classifieror the like. When manufacturing LSCF as a complex oxide, the specificsurface area is adjusted to 3 m²/g to 12 m²/g.

2-2 Method of Manufacture of Electrode Material using Liquid-PhaseMethod

FIG. 2 is a flowchart describing a method of manufacturing an electrodematerial using a liquid-phase method.

Firstly, in step S201, a starting material is prepared corresponding tothe type of complex oxide. When manufacturing LSCF as the complex oxideby use of a co-precipitation method or citrate method, La(NO₃)₃.6H₂O,Sr(NO₃)₂, Co(NO₃)₃.9H₂O and Fe(NO₃)₃.9H₂O are prepared. The averageparticle diameter of La(NO₃)₃.6H₂O may be 0.3 micrometers to 0.6micrometers, the average particle diameter of Sr(NO₃)₂ may be 0.1micrometers to 0.4 micrometers, the average particle diameter ofCo(NO₃)₃.9H₂O may be 0.2 micrometers to 0.5 micrometers, and the averageparticle diameter of Fe(NO₃)₃.9H₂O may be 0.3 micrometers to 0.8micrometers. When manufacturing LSCF using a Pechini method, La₂O₃,SrO₃, Co₃O₄ and Fe(NO₃)₃.9H₂O are prepared to have the above averageparticle diameter. Furthermore, controlling the particle sizedistribution of the starting materials is important. More specifically,it is desirable to remove coarse particles of greater than or equal to15 micrometers in advance by use of an air classifier. The removal ofcoarse particles is effective for uniformity when executing mixing andsynthesizing (calcinating) in subsequent steps.

Next, in step S202, the starting materials are classified. Morespecifically, for example, the specific surface area of each startingmaterial is adjusted by classification using an air classifier. Whenmanufacturing LSCF as a complex oxide by use of co-precipitation or acitrate method, the specific surface area of La(NO₃)₃.6H₂O is adjustedto 2 m²/g-8 m²/g, the specific surface area of Sr(NO₃)₂ is adjusted to 1m²/g-5 m²/g, the specific surface area of Co(NO₃)₃.9H₂O is adjusted to 2m²/g-5 m²/g, and the specific surface area of Fe(NO₃)₃.9H₂O is adjustedto 3 m²/g-10 m²/g.

Next, in a step S203, the respective starting materials are mixed at apredetermined mixing ratio. More specifically, when manufacturing LSCFby use of co-precipitation, after dissolving the starting materials in apure state to prepare a 0.2 M aqueous solution, an aqueous nitratesolution is added while stirring in a precipitation agent. Whenpreparing the LSCF using a citrate method, the respective startingmaterials are dissolved in a pure state and citric acid is added untilall the metal is precipitated, and the viscosity is adjusted by use ofheating after immersion to approximately 60 degrees C. to dehydrate.When preparing LSCF using a Pechini method, after preparing an aqueousnitrate solution for each of the starting materials and mixing allsolutions, citric acid and ethylene glycol are added.

In this mixing process, it is preferred to add a predetermined additiveto the respective starting materials. The additives are phosphorus (P),chrome (Cr), and boron (B). The concentration of P contained in theadditive is preferably at least 1 ppm to no more than 50 ppm in a weightratio relative to the starting materials, and more preferably at least 1ppm and no more than 30 ppm. The concentration of Cr contained in theadditive is preferably at least 1 ppm to no more than 500 ppm in aweight ratio relative to the starting materials, and more preferably atleast 1 ppm and no more than 100 ppm. The concentration of B containedin the additive is preferably at least 1 ppm to no more than 50 ppm in aweight ratio relative to the starting materials, and more preferably atleast 1 ppm and no more than 10 ppm. The additives have the function ofcreating a uniform dispersion and mixture in the constituent components,or during thermal synthesis processes, and non-uniformity in each of theelements (for example, resulting from phase splitting, heterogeneousphase precipitation, or the like) can be inhibited as a result of theseadditives. As a result, uniformity of the composition distribution ofthe electrode material is enabled by suitable control of the addedamount of the additives.

Next, in step S204, the aqueous solution prepared in step 5203 is dried.When using co-precipitation, vacuum drying is used at approximately 110degrees C., when using a citrate method, drying is performed atapproximately 70 degrees C., and when using a Pechini method, drying isperformed at approximately 200 degrees C.

Next, in step S205, the electrode material is synthesized by firing ofthe dried starting materials. The synthesis conditions are suitablyadjusted within a range of a synthesis temperature of 900 degrees C. to1400 degrees C. and a synthesis time of 1 to 30 hrs in an oxidizingatmosphere.

Next, in step S206, the electrode material that is in a configuration ofa synthesized agglomerate is subjected to comminution. In step S207, theelectrode material after comminution is classified. The details of thesesteps are the same as steps S105 and S106 described above.

3. Vertically-Striped Fuel Cell (Solid Oxide Fuel Cell)

A solid oxide fuel cell is an example of a fuel cell. In particular, aSOFC will be mainly described that has a cell stack structure in which aplurality of fuel cells are stacked.

3.1 Overview of Fuel Cell

As illustrated in FIG. 3, the fuel cell 10 includes a fuel cell(hereinafter simply referred to as “cell”) 1, and a current collectingmember 4.

3-2 Overview of Cell 1

The cell 1 is a thin ceramic plate. The thickness of the cell 1 is forexample 30 micrometers to 700 micrometers, and the diameter of the cell1 is for example 5 mm to 50 mm. The cell 1 as illustrated in FIG. 3includes an anode 11, a barrier layer 13, a cathode 14, and anelectrolyte layer 15 (solid electrolyte layer).

3-3 Anode

The material used in the anode 11 for example includes a material usedin the formation of the anode in a known fuel cell. More specifically,the material used in the anode 11 may include NiO—YSZ (nickeloxide—yttria-stabilized zirconia) and/or NiO—Y₂O₃ (nickel oxide—yttria).The anode 11 may include these materials as a main component. The anode11 functions as the anode.

Furthermore, the anode 11 may function as a base plate that supports theother layers included in the cell 1 (in other words, a support body).That is to say, the thickness of the anode 11 may have the maximumthickness of the plurality of layers contained in the cell 1. Morespecifically, the thickness of the anode 11 is of the order of 10micrometers to 600 micrometers.

The anode 11 can be imparted with conductive properties by applicationof a reduction treatment (for example, a treatment of reducing NiO toNi).

The anode 11 may include at least two layers. For example, the anode 11may have two layers, that is to say, a base plate and an anode-activelayer (fuel-side electrode) formed thereon. The material in the baseplate is configured by a material that includes properties such aselectron conductivity. The anode-active layer is configured by amaterial that includes properties such as electron conductivity andproperties such as oxidizing ion (oxygen ion) conductivity. The“proportion of the volume of material that has oxidizing ion (oxygenion) conductivity relative to the total volume excluding the pores” inthe anode active layer is greater than the “proportion of the volume ofmaterial that has oxidizing ion (oxygen ion) conductivity relative tothe total volume excluding the pores” in the base plate. The material inthe base plate and the anode active layer can be selected from thematerials for the anode 11 described above. More specifically, acombination is possible of a base plate configured from NiO—Y₂O₃ and theanode active layer configured by NiO—YSZ.

3-4 Barrier Layer

The barrier layer 13 is provided between the cathode 14 and the anode11, and more specifically, is provided between the cathode 14 and theelectrolyte layer 15.

The barrier layer 13 includes cerium. The barrier layer may includecerium as the ceria (cerium oxide). More specifically, materials thatare used in the barrier layer 13 include ceria and ceria-based materialsincluding rare-earth metal oxides configured as a solid solution inceria. The barrier layer 13 may include a ceria-based material as a maincomponent.

More specifically, the ceria-based material includes GDC ((Ce, Gd)O₂:gadolinium doped ceria), and SDC ((Ce, Sm)O₂: samarium doped ceria). Theconcentration of the rare earth metal in the ceria-based material ispreferably 5 to 20 mol %. The barrier layer 13 may include an additivein addition to a ceria-based material.

The thickness of the barrier layer 13 is no more than 30 micrometers.

The barrier layer 13 suppresses the diffusion of cations from thecathode 14 into the electrolyte layer 15. As a result, the barrier layer13 enables suppression of a reduction in the output density, andincreases the product life of the cell 1.

3-5 Cathode

The cathode 14 is configured using electrode materials as described in“Section 1.” above. This type of cathode 14 preferably includes anadditive (P, Cr, and B) at a predetermined weight ratio relative to thetotal weight of the electrode material. In this configuration, thecontent amount of P is preferably at least 1 ppm to no more than 50 ppmin a weight ratio relative to the starting materials, and morepreferably at least 1 ppm and no more than 30 ppm. The content amount ofCr is preferably at least 1 ppm to no more than 500 ppm in a weightratio relative to the starting materials, and more preferably at least 1ppm and no more than 100 ppm. The content amount of B is preferably atleast 1 ppm to no more than 50 ppm in a weight ratio relative to thestarting materials, and more preferably at least 1 ppm and no more than10 ppm.

The thickness of the cathode 14 may be of the order of 5 micrometers to50 micrometers.

3-6 Electrolyte Layer

The electrolyte layer 15 is provided between the barrier layer 13 andthe anode 11. The electrolyte layer 15 includes zirconium. Theelectrolyte layer 15 may include zirconium in the form of zirconia(ZrO₂). More specifically, the electrolyte layer 15 may include zirconiaas a main component. The electrolyte layer 15 may include an additivesuch as Y₂O₃ and/or Sc₂O₃ in addition to zirconia. These additives mayfunction as a stabilizer. The added amount of the additive in theelectrolyte layer 15 is of the order of 3 to 20 mol %. In other words,the material used in the electrolyte layer 15 includes yttria-stabilizedzirconia such as 3YSZ, 8YSZ, and 10YSZ or zirconia-based materials suchas ScSZ (scandia-stablized zirconia).

The thickness of the electrolyte layer 15 may be no more than 30micrometers.

3-7 Current Collecting Member

A current collecting member 4 includes a plurality of conductiveconnection portions 41.

As illustrated in FIG. 3, the conductive connection portions 41 areconfigured as an depressed portion provided in the current collectingmember 4, and the bottom portion thereof is connected through aconductive adhesive 411 to the cathode 14. The bottom portion of theconductive connection portions 411 includes a periphery and anon-connected position.

During power generation, fuel gas is supplied to the anode 11. Thesupply of air to the cathode 14 draws air from the side surface of thecell stack structure (for example, the front of the face of the page inFIG. 3).

Although this is not shown, the fuel cell 10 further includes a membersuch as a lead that sends a current generated by the cell stack to anexternal apparatus, and a gas reforming unit that includes a catalyst orthe like for reforming the fuel gas.

4. Method of Manufacturing Fuel Cell 4-1 Formation of Anode

The anode 11 can be formed by powder compaction. That is to say, theanode 11 may include the feature of introducing powder, in whichmaterial for the anode 11 is mixed, into a mold, and compressing tothereby mold a compacted powder body.

The material for the anode 11 may be configured according to thedescription above in relation to the configuration of the fuel cell. Thematerial includes use of nickel oxide, zirconia and a pore forming agentas required. A pore forming agent is an additive that forms pores in theanode. The pore forming agent includes use of a material that is removedin later processing steps. Examples of such materials include cellulosepowder.

This is no particular limitation on the mixing ratio of the material,and the mixing ratio may be suitably set in response to thecharacteristics or the like required by the fuel cell.

The pressure applied to the powder during powder compaction molding isset to impart sufficient rigidity to the anode.

The internal structure of the anode 11 such as the gas conduit (notshown) is formed by powder compaction molding in a configuration inwhich a member that is removed by firing (a cellulose sheet or the like)is disposed in an inner portion of the powder body and then firing isperformed.

4-2 Formation of Electrolyte Layer

The method of manufacturing the fuel cell includes formation of theelectrolyte layer on a molded body of the anode formed by powdercompaction.

The method of formation of the electrolyte is a method such as CIP (coldisostatic pressing) that uses an electrolyte material that is processedinto a sheet configuration, or thermo-compression bonding. Otherwise, aslurry dip method may be used in which the anode is immersed into anelectrolyte material adjusted to a slurry configuration. When using theCIP method, the pressure during the pressing operation on the sheet ispreferably 50 to 300 MPa.

4-3 Firing

The method of manufacturing the fuel cell includes co-firing(co-sintering) of the electrolyte layer and the anode formed by powdercompaction. The temperature and the time for firing are set in responseto the cell material.

4-4 Degreasing

Degreasing may be performed prior to firing in 4-3. The degreasing isexecuted by heating. The conditions such as temperature and time are setin response to the material of the cell or the like.

4-5 Formation of Cathode

The cathode is formed by firing after formation of a layer of materialfor the cathode by a printing method, powder compaction or the like on astacked body of the barrier layer, the electrolyte layer and the anode.More specifically, in case of an electrode material configured fromLSCF, when using a printing method, a paste prepared by mixing LSCFtogether with a binder, dispersal agent and dispersal medium is printedonto the stacked body and fired (firing temperature 900 degrees C. to1100 degrees C., and firing time 1 hr to 10 hrs).

4-6 Other Processing Steps

Other steps may be included in the manufacturing method depending on theconfiguration of the fuel cell. For example, the manufacturing methodmay include a step of providing a reaction prevention layer between theelectrolyte layer and the cathode, or may include a step of forming adouble layered structure in the anode (a step of forming the base plateand a step of forming the anode active layer).

5. Segmented-in-Series Fuel Cell

The fuel cell 10 described above includes a plurality of stacked cells 1and a current collecting member 4 connecting the cells 1 electrically.In other words, the fuel cell 10 is a vertically-striped fuel cell.However, the technique disclosed herein may also be applied to asegmented-in-series fuel cell. A segmented-in-series fuel cell will bedescribed below.

The segmented-in-series fuel cell (hereinafter simply referred to as a“fuel cell”) 100 includes a support base plate 102, an anode 103, anelectrolyte layer 104, a cathode 106, an interconnector 107, a currentcollecting unit 108, and a barrier layer 13. The fuel cell 100 includesa plurality of cells 110. Those component elements that are the same asthe component elements already described above are denoted by the samereference numerals, and such description will not be repeated. In FIG.6, for sake of convenience of description, the current collecting unit108 is not illustrated.

The fuel cell 100 includes the cells 110 disposed on the support baseplate 102 and an interconnector 107 that electrically connects the cells110. The cells 110 are units that include an anode 103 and a cathode 106that corresponds to the anode 103. More specifically, the cells 110include an anode 103, an electrolyte layer 104 and a cathode 106 stackedin the thickness direction (y axis direction) of the support base plate102. The anode 103, the electrolyte layer 104 and the cathode 106configure the power generation element of the cell 110.

The support base plate 102 is flat and elongated in one direction (zaxis direction). The support base plate 102 is a porous body that haselectrical insulating properties. The support base plate 102 may includenickel. More specifically, the support base plate 102 may containNi—Y₂O₃ (nickel yttria) as a main component. The nickel may be includedas an oxide (NiO). During power generation, NiO may be reduced to Ni byhydrogen gas.

As illustrated in FIG. 6 and FIG. 7, a conduit 123 is provided in aninner portion of the support base plate 102. The conduit 123 extendsalong the longitudinal direction (z axis direction) of the support baseplate 102. During power generation, fuel gas flows into the conduit 123,through a hole that is provided in the support base plate 102 to therebysupply fuel gas to the anode 103 described below.

The anode 103 is provided on the support base plate 102. A plurality ofanodes 103 is disposed on a single support base plate 102 and isarranged in the longitudinal direction (z axial direction) of thesupport base plate 102. That is to say, a space is provided betweenadjacent anodes 103 with respect to the longitudinal direction (z axisdirection) of the support base plate 102.

The composition of the anode 103 may be the same as the composition ofthe anode 11.

The anode 103 may include an anode current collecting layer and an anodeactive layer. The anode current collecting layer is provided on thesupport base plate 102, and the anode active layer is provided on theanode current collecting layer while avoiding superimposition withrespect to the interconnector 107.

The anode 103 may include an anode current collecting layer and an anodeactive layer. The anode current collecting layer is provided on thesupport base plate 102 and the anode active layer is provided on theanode current collecting layer. The composition of the anode currentcollecting layer and the anode active layer has been described above.

The electrolyte layer 104 is also termed a solid electrolyte layer. Asillustrated in FIG. 7, the electrolyte layer 104 is provided on theanode 103. In a region that is not provided with the anode 103 on thesupport base plate 102, the electrolyte layer 104 may be provided on thesupport base plate 102.

The electrolyte layer 104 includes a non-connected position in thelongitudinal direction (z axis direction) of the support base plate 102.In other words, a plurality of electrolyte layers 104 is disposed at aninterval in the z axis direction. Namely, a plurality of electrolytelayers 104 is provided along the longitudinal direction (z axisdirection) of a single support base plate 102.

Electrolyte layers 104 adjacent in the z axis direction are connected byan interconnector 107. In other words, the electrolyte layers 104 areconnected from an interconnector 107 to an interconnector 107 that isadjacent to that interconnector 107 in the longitudinal direction (zaxis direction) of the support base plate 102. The interconnector 107and the electrolyte layer 104 have a dense structure in comparison tothe support base plate 102 and the anode 103. Therefore, theinterconnector 107 and the electrolyte layer 104 function as a sealingportion that partitions air and fuel gas by the provision of a connectedstructure in the z axis direction in the fuel cell 100.

The composition of the electrolyte layer 104 may include a compositionthat is the same as the electrolyte layer 15 as described above.

The same description provided in relation to the vertical-striped fuelcell applies to the configuration of the barrier layer 13. The barrierlayer 13 is provided between the cathode 106 and the electrolyte layer104.

The cathode 106 is disposed on the barrier layer 13 without projectingfrom the outer edge of the barrier layer 13. One cathode 106 is stackedon one anode 103. That is to say, a plurality of cathodes 106 isprovided along the longitudinal direction (z axis direction) of thesupport base plate 102 on a single support base plate 102.

The composition of the cathode 106 is configured with the electrodematerial described in “Section 1.” above in the same manner as thecathode 14 described above. The cathode 106 preferably includes anadditive (P, Cr, and B) at a predetermined weight ratio relative to thetotal weight of the electrode material in the same manner as the cathode15 of the vertically-striped fuel cell described above. In thisconfiguration, the content amount of P is preferably at least 1 ppm tono more than 50 ppm in a weight ratio relative to the startingmaterials, and more preferably at least 1 ppm and no more than 30 ppm.The content amount of Cr is preferably at least 1 ppm to no more than500 ppm in a weight ratio relative to the starting materials, and morepreferably at least 1 ppm and no more than 100 ppm. The content amountof B is preferably at least 1 ppm to no more than 50 ppm in a weightratio relative to the starting materials, and more preferably at least 1ppm and no more than 10 ppm.

As described above, the interconnector 107 may be disposed to configureelectrical contact between the cells 110. In FIG. 7, the interconnector107 is stacked onto the anode 103.

In the present specification, “stack” includes the disposition of twoelements in connection, and a disposition that provides an overlap inthe y axis direction although there is not a connection.

In FIG. 7, as described above, the interconnector 107 is disposed tospan the interval between the electrolyte layers 104 in the longitudinaldirection (z axis direction) of the support base plate 102. In thismanner, cells 110 that are adjacent in the longitudinal direction (zaxis direction) of the support base plate 102 are electricallyconnected.

The interconnector 107 configures an electrode that is used for theelectrical connection between the plurality of cells 110. Morespecifically, the interconnector 107 illustrated in FIG. 7 functions asan electrode for the cells 110 disposed on the right side of FIG. 7.

The interconnector 107 that configures the electrode as described aboveis configured using the electrode material described in “Section 1.”above in the same manner as the cathode 106 described above.

That is to say, the interconnector 107 includes a main component of aperovskite complex oxide as a main component. In particular, achromite-based material such as lanthanum chromite (LaCrO₃) is anexample of a perovskite complex oxide used in the interconnector 107.

The composition formula for the lanthanum chromite is expressed bygeneral formula (1) below.

Ln_(1-x)A_(x)Cr_(1-y-z)B_(y)O₃   (1)

In Formula (1), wherein Ln is at least one type of element selected fromthe group of Y and a lanthanoid, A is at least one type of elementselected from the group of Ca, Sr and Ba, and B is at least one type ofelement selected from the group of Ti, V, Mn, Fe, Co, Cu, Ni, Zn, Mg andAl, and wherein 0.025≦x≦0.3, 0≦y≦0.22, 0≦z≦0.15.

Lanthanum chromite is a material that can stably exist under both anatmospheric and reducing atmosphere at the operating temperature (600 to1000 degrees C.) of the SOFC, and is preferably used as aninterconnector material (electrode material) of an SOFC cell thatincludes horizontal stripes.

However, it is known that lanthanum chromite is a sintering resistantmaterial, and addition is required of an additive that facilitatesfiring, such as a sintering agent (CaO, SrO, or the like), to co-sinterwith the support base plate 102, the anode 103 and the electrolyte layer104 for application to the SOFC cell.

As a result, as described above, a highly uniform compositiondistribution is preferred also in the interconnector material (electrodematerial) to which the sintering agent is added. More specifically, avalue of the standard deviation for the atomic percentage of respectiveelements contained at the A site are acquired by use of energydispersive X-ray spectroscopy (EDS) at 10 spots in an arbitrary field inthe electrode material is preferably no more than 10.3.

In this manner, since the overall interconnector 107 can be impartedwith a dense configuration, the localized occurrence of a region ofinsufficient firing (pinholes) in the interconnector 107 can besuppressed. As a result, it is possible to improve the reliability ofthe interconnector 107.

The current collecting unit 108 is disposed to electrically connect theinterconnector 107 and the cell 110. More specifically, the currentcollecting unit 108 is provides a connection from the cathode 106 to theinterconnector 107 that is included in the cell 110 that is adjacent tothe cell 110 that includes the cathode 106. The current collecting unit108 may include conductive properties.

The cathode 106 that is included in the cell 110 is electricallyconnected to the anode 103 of the adjacent cell 110 through the currentcollecting unit 108 and the interconnector 107. That is to say, thecurrent collecting unit 108 participates in the connection between cells110 in addition to the interconnector 107.

The specific dimensions of each component of the fuel cell 100 may beset as shown below.

Width W1 of support base plate 102: 1 to 10 cm

Thickness W2 of support base plate 102: 1 to 10 mm

Length W3 of support base plate 102: 5 to 50 cm

Distance W4 from outer surface of support base plate 102 (interfacebetween support base plate 102 and anode) to conduit 123: 0.1-4 mm

Thickness of Anode 103: 50-500 micrometers (When the anode 103 includesan anode current collecting layer and an anode active layer: thicknessof anode current collecting layer: 50-500 micrometers, thickness ofanode active layer: 5-30 micrometers)

Thickness of electrolyte layer 104: 3-50 micrometers

Thickness of cathode 106: 10-100 micrometers

Thickness of interconnector 107: 10-100 micrometers

Thickness of current collecting unit 108: 50-500 micrometers

The dimensions described in relation to a vertically-striped fuel cellmay be adopted for the constituent elements that are not specificallydisclosed. However it goes without saying that the technique hereindisclosed is not limited to these values.

(Additional Note)

The cathode material of the solid oxide fuel cell includes a complexoxide material that has a perovskite structure expressed by the generalformula ABO₃. The complex oxide is preferably such that P is at least 1ppm and no more than 50 ppm, Cr is at least 1 ppm and no more than 500ppm, and B is at least 1 ppm and no more than 50 ppm in a weight ratiorelative to the total weight of the complex oxide.

In the cathode material, the content amount of P included in the complexoxide is more preferably no more than 30 ppm in a weight ratio relativeto the total weight of the complex oxide.

In the cathode material, the content amount of Cr included in thecomplex oxide is more preferably no more than 100 ppm in a weight ratiorelative to the total weight of the complex oxide.

In the cathode material, the content amount of B included in the complexoxide is more preferably no more than 10 ppm in a weight ratio relativeto the total weight of the complex oxide.

In the cathode material, the respective content amount of P, Cr and B inthe complex oxide is preferably at least 1 ppm.

EXAMPLES A. Preparation of Cell

An NiO-8YSZ anode active layer (10 micrometers), an 8YSZ electrolytelayer (3 micrometers) and a GDC barrier layer (3 micrometers) arestacked on an NiO-8YSZ anode base plate (500 micrometers), and firedunder conditions of 1400 degrees C. for 2 hours.

As illustrated in Table 1 to Table 3, 10 types of electrode materials(No. 1 to No. 10) including (La_(0.6)Sr_(0.4))(Co_(0.2)Fe_(0.8))O₃, 6types of electrode materials (No. 11 to No. 16) including(La_(0.8)Sr_(0.2))FeO₃, and 6 types of electrode materials (No. 17 toNo. 22) including (Ni_(0.6)Fe_(0.4))O₃ were obtained. Then asillustrated in Table 10, 6 types of electrode materials (No. 23 to No.28) including (La_(0.6)Sr_(0.4))(Co_(0.2)Fe_(0.8))O₃ in the same manneras No. 1 to No. 10 were obtained. However, no additives were activelyadded to No. 28. ICP analysis is used to confirm that the added amountof the additive (at least one of P, Cr and B) during electrode operationcorresponds to the content amount of the additive in the electrodematerial after calcination (synthesis).

Those electrode materials that are expressed using the same generalformula but denoted by different reference numerals differ in relationto starting materials, firing conditions, or comminution conditions.Furthermore, the tables indicate whether each electrode material wassynthesized using a solid phase method or a liquid phase method.Furthermore, the content amount of the additive (P, Cr or B) included inthe electrode material is disclosed in the table.

The average particle diameter of the resulting disintegrated product is200 micrometers. The disintegrated product was used in the measurementof the composition distribution described below.

The disintegrated product was subjected to comminution using a ball millapparatus. The average particle diameter of the electrode material(powder) was all no more than 1.0 micrometer upon measurement using alaser diffraction/scattering type particle size distribution measurementapparatus (LA-700 manufactured by Horiba Ltd.).

A paste was prepared using the resulting powder and the paste was usedto form a film with a screen printing method resulting in a cathode (30micrometers) on the barrier layer. The cathode was attached by firingonto the barrier layer by heating to no more than 1000 degrees C. for 2hours.

SOFCs were obtained in the above manner.

B. Evaluation B-1 Measurement of Composition Distribution

The atomic percentage distribution of each element in the disintegratedproduct formed of electrode material was measured using EPMA. Morespecifically, measurements are performing using an electron probe microanalyzer manufactured by JEOL Ltd. (model: JXA-8500F). Next, in anarbitrary field, EDS is used to measure the atomic percentage (mol %) ofan oxide of each element at the A site and each element at the B site inrelation to 10 spots in a section not forming a cavity that can beidentified in an SEM image. More specifically, measurements wereperformed using a field emission scanning electron microscope (model:ULTRA55) manufactured by Zeiss AG (Germany).

Then, the respective concentration of La and Sr at the A site wasmeasured at 10 spots in relation to each of the samples No. 1 to No. 10to obtain an average value for the La concentration and the standarddeviation of the La concentration at each spot and the average value forthe Sr concentration and the standard deviation of the Sr concentrationat each spot. In the same manner a concentration average value and astandard deviation for the concentration at each spot were obtained forCo and Fe at the B site. Furthermore, the maximum value of the standarddeviation in relation to the atomic percentage of elements at the A siteand the maximum value of the standard deviation in relation to theatomic percentage of elements at the B site were obtained for eachsample No. 1 to No. 10.

The same operation was performed in relation to the concentration of Feat the B site and La and Sr at the A site for each sample No. 11 to No.16, and the same operation was performed in relation to theconcentration of Fe and Ni at the B site and La at the A site for eachsample No. 17 to No. 22.

B-2 Durability Experiments

Continuous power generation was performed using the prepared SOFC cell.The voltage drop rate (deterioration rate) was calculated per 1000 hoursusing power generation conditions of 750 degrees C. and current density:0.3 A/cm². A deterioration rate of no more than 1% was evaluated as“good”.

C Results

C-1 No. 1 to No. 10: (La_(0.6)Sr_(0.4))(Co_(0.2)Fe_(0.8))O₃

In relation to the samples No. 1 to No. 10, the measurement results forthe concentration of No. 1 sample as an example and the results of thecalculation of the average value and the standard deviation are shown inTable 1. Table 2 shows the maximum value of the standard deviation forthe atomic percentage of each element in relation to samples No. 1 toNo. 10. The maximum value of the standard deviation at the A site andthe maximum value of the standard deviation at the B site are underlinedin relation to each sample. Table 3 shows the maximum value of thestandard deviation at the A site and the maximum value of the standarddeviation at the B site shown in Table 2, the voltage drop rate(deterioration rate) per 1000 hours, and the evaluation result based onthe voltage drop rate for samples No. 1 to No. 10.

FIG. 4 and FIG. 5 show respective SEM images and concentration mappingimages for the same field in relation to samples No. 1 and No. 7. InFIG. 4 and FIG. 5, the actual positions of high atomic percentage areshown by a red color and positions of low atomic percentage are shownwith a blue color.

TABLE 1 Concentration Analysis Results for 10 Spots in Sample No. 1 of(La_(0.6)Sr_(0.4))(Co_(0.2)Fe_(0.8))O₃ Analysis Spot La (mol %) Sr (mol%) Co (mol %) Fe (mol %) 1 17.1 30.9 6.9 45.1 2 19.4 28.7 6.5 45.4 324.4 22.3 7.9 45.4 4 24.1 22.5 8.6 44.8 5 22.1 28.8 7.7 42.1 6 29.7 20.19.1 41.1 7 32.5 22.5 10.3 34.7 8 38.3 16.8 9.5 35.4 9 25.6 20.3 10.443.7 10  19.5 26.8 7.3 46.4 Average Value 25.27 23.97 8.35 42.41Standard Deviation 6.23 4.34 1.36 3.99

TABLE 2 Maximum Value for Standard Deviation and Additive Content Amountfor Samples No. 1 to No. 10 of (La_(0.6)Sr_(0.4))(Co_(0.2)Fe_(0.8))O₃Standard Deviation Additive content amount Sample Synthesis A site Bsite (ppm) No. Method La Sr Co Fe P Cr B 1 Solid phase 6.23 4.34 1.363.99 40 400 30 method 2 Solid phase 3.12 4.11 0.82 1.54 35 300 20 method3 Solid phase 10.3  8.32 2.87 3.61 50 500 50 method 4 Solid phase 1.560.89 0.68 0.56 40 250 20 method 5 Solid phase 7.52 13.2  4.98 2.86 70800 80 method 6 Solid phase 11.5  6.32 3.15 4.88 60 630 60 method 7Liquid phase 0.05 0.04 0.1  0.05 20 20 3 method 8 Liquid phase 0.27 0.460   0.07 30 100 5 method 9 Liquid phase 1.13 1.03 0.68 0.36 45 460 50method 10 Liquid phase 0.2  0.25 0.03 0.05 20 60 10 method

TABLE 3 Evaluation Result for Deterioration Rate and Maximum Value ofStandard Deviation in Samples No. 1 to No. 10 of(La_(0.6)Sr_(0.4))(Co_(0.2)Fe_(0.8))O₃ Maximum Value Maximum ValueDeterioration Evalua- Sample Standard Standard Rate tion No. Deviationat A site Deviation at B site (%/1000 hr) Result 1 6.23 3.99 0.76 Good 24.11 1.54 0.63 Good 3 10.3 3.61 0.95 Good 4 1.56 0.68 0.65 Good 5 13.24.98 1.85 Poor 6 11.5 4.88 1.52 Poor 7 0.05 0.10 0.30 Good 8 0.46 0.070.52 Good 9 1.13 0.68 0.87 Good 10  0.25 0.05 0.45 Good

As illustrated in FIG. 4 to FIG. 5 and Table 1 to Table 3, thedeterioration rate was suppressed to a small value for samples No. 1 toNo. 4, and No. 7 to No. 10. These samples exhibit a standard deviation(scattering) for the atomic percentage of elements at the A site of lessthan 11.5, more specifically, the value was no more than 10.3. Thestandard deviation for the atomic percentage of elements at the B sitewas no more than 3.99.

In samples No. 5 and No. 6 which exhibited a large deterioration rate,the standard deviation for the atomic percentage of elements at the Asite was at least 11.5, and the standard deviation for the atomicpercentage of elements at the B site was at least 4.88.

C-2 No. 11 to No. 16: (La_(0.8)Sr_(0.2))FeO₃

In relation to the samples No. 11 to No. 16, the measurement resultsusing the concentration of No. 11 sample as an example, and the resultsof the calculation of the average value and the standard deviation areshown in Table 4. Table 5 shows the maximum value of the standarddeviation for the atomic percentage of each element in relation tosamples No. 11 to No. 16. The maximum value of the standard deviation atthe A site and the maximum value of the standard deviation at the B siteare underlined in relation to each sample. Table 6 shows the maximumvalue of the standard deviation at the A site and the maximum value ofthe standard deviation at the B site shown in Table 5, the voltage droprate (deterioration rate) per 1000 hours, and the evaluation resultsbased on the voltage drop rate for samples No. 11 to No. 16.

TABLE 4 Concentration Analysis Results for 10 Spots in Sample No. 11 of(La_(0.8)Sr_(0.2))FeO₃ Analysis Spot La (mol %) Sr (mol %) Fe (mol %) 136.4 8.8 54.8 2 35.9 9.1 55.0 3 30.5 11.4 58.1 4 36.1 8.8 55.1 5 41.86.5 51.7 6 36.9 8.5 54.6 7 49.7 6.1 44.2 8 28.2 11.1 60.7 9 36.8 8.754.5 10  42.0 6.6 51.4 Average Value 37.43 8.56 54.01 Standard Deviation5.74 1.71 4.16

TABLE 5 Maximum Value for Standard Deviation and Additive Content Amountfor Samples No. 11 to No. 16 of (La_(0.8)Sr_(0.2))FeO₃ StandardDeviation Synthesis A site B site Additive content amount (ppm) SampleNo. Method La Sr Fe P Cr B 11 Solid phase 5.74 1.71 4.16 20 100 10method 12 Solid phase 4.28 2.95 3.25 30 300 20 method 13 Solid phase7.91 2.77 3.68 50 500 50 method 14 Solid phase 10.95  2.65 4.98 60 55070 method 15 Liquid phase 1.04 1.73 0.65 20 80 10 method 16 Liquid phase0.43 0.09 0.21 10 30 5 method

TABLE 6 Evaluation Result for Deterioration Rate and Maximum Value ofStandard Deviation in Samples No. 11 to No. 16 of (La_(0.8)Sr_(0.2))FeO₃Maximum Value Maximum Value Deteriora- Evalua- Sample Standard Standardtion Rate tion No. Deviation at A site Deviation at B site (%/1000 hr)Result 11 5.74 4.16 0.34 Good 12 4.28 3.25 0.42 Good 13 7.91 3.68 0.55Good 14 10.95 4.98 1.23 Poor 15 1.73 0.65 0.32 Good 16 0.43 0.21 0.22Good

As illustrated in Table 4 to Table 6, the deterioration rate wassuppressed to a small value for samples No. 11 to No. 13, No. 15 and No.16. These samples exhibit a standard deviation (scattering) for theatomic percentage of elements at the A site of no more than 7.91, andthe standard deviation for the atomic percentage of elements at the Bsite was no more than 4.16.

In sample No. 14 which exhibited a large deterioration rate, thestandard deviation for the atomic percentage of elements at the A sitewas at least 10.95. In sample No. 14, the standard deviation for theatomic percentage of elements at the B site was comparatively large at4.98.

C-3 No. 17 to No. 22: La(Ni_(0.6)Fe_(0.4))O₃

In relation to the samples No. 17 to No. 22, the measurement resultsusing the concentration of No. 17 sample as an example, and the resultsof the calculation of the average value and the standard deviation areshown in Table 7. Table 8 shows the maximum value of the standarddeviation for the atomic percentage of each element in relation tosamples No. 17 to No. 22. The maximum value of the standard deviation atthe A site and the maximum value of the standard deviation at the B siteare underlined in relation to each sample. Table 9 shows the maximumvalue of the standard deviation at the A site and the maximum value ofthe standard deviation at the B site shown in Table 8, the voltage droprate (deterioration rate) per 1000 hours, and the evaluation resultsbased on the voltage drop rate for samples No. 17 to No. 22.

TABLE 7 Concentration Analysis Results for 10 Spots in Sample No. 17 ofLa(Ni_(0.6)Fe_(0.4))O₃ Analysis Point La (mol %) Ni (mol %) Fe (mol %) 140.3 28.7 31.0 2 37.4 33.9 28.7 3 48.7 31.5 19.8 4 58.1 25.4 16.5 5 41.832.0 26.2 6 40.9 34.8 24.3 7 42.1 29.9 28.0 8 59.2 23.9 16.9 9 35.7 36.427.9 10  47.9 28.9 23.2 Average Value 45.21 30.54 24.25 StandardDeviation 7.72 3.79 4.81

TABLE 8 Maximum Value for Standard Deviation and Additive Content Amountfor Samples No. 17 to No. 22 of La(Ni_(0.6)Fe_(0.4))O₃ StandardDeviation Synthesis A site B site Additive content amount (ppm) SampleNo. Method La Ni Fe P Cr B 17 Solid phase 7.72 3.79 4.81 40 400 50method 18 Solid phase 10.5  6.35 1.23 60 600 60 method 19 Solid phase5.23 4.35 2.35 50 500 30 method 20 Solid phase 3.52 4.23 1.85 30 250 20method 21 Liquid phase 1.35 1.23 0.85 20 100 10 method 22 Liquid phase0.35 0.33 0.36 10 50 5 method

TABLE 9 Evaluation Result for Deterioration Rate and Maximum Value ofStandard Deviation in Samples No. 17 to No. 22 of La(Ni_(0.6)Fe_(0.4))O₃Maximum Value Maximum Value Deteriora- Evalua- Sample Standard Standardtion Rate tion No. Deviation at A site Deviation at B site (%/1000 hr)Result 17 7.72 4.81 0.78 Good 18 10.5 6.35 1.65 Poor 19 5.23 4.35 0.75Good 20 3.52 4.23 0.68 Good 21 1.35 1.23 0.46 Good 22 0.35 0.36 0.45Good

As illustrated in Table 7 to Table 9, the deterioration rate wassuppressed to a small value for samples No. 17, No. 19 to No. 22. Thesesamples exhibit a standard deviation (scattering) for the atomicpercentage of elements at the A site of no more than 7.72. These samplesexhibit the standard deviation for the atomic percentage of elements atthe B site was no more than 4.81.

On the other hand, the standard deviation for the atomic percentage ofelements at the A site in sample No. 18 which exhibited a largedeterioration rate was relatively large at 10.5, and the standarddeviation for the atomic percentage of elements at the B site was alsocomparatively large at 6.35.

C-4 No. 23 to No. 28: (La_(0.6)Sr_(0.4))(Co_(0.2)Fe_(0.8))O₃

Table 10 shows the measurement results for the voltage drop rate(deterioration rate) per 1000 hours and the concentration of theadditive (P, Cr and B) for Samples No. 23 to No. 28.

TABLE 10 Additive content Deterioration Sample Synthesis amount (ppm)Rate Evaluation No. Method P Cr B (%/1000 hr) Result 23 Solid phase 60530 75 1.66 Poor (x) method 24 Liquid phase 50 500 50 0.65 Good (∘)method 25 Solid phase 40 250 25 0.56 Good (∘) method 26 Liquid phase 30100 10 0.38 Good (⊚) method 27 Liquid phase 15 65 5 0.23 Good (⊚) method28 Liquid phase less less less 1.23 Poor (x) method than 1 than 1 than 1

As illustrated in Table 10, the deterioration rate was not suppressed toa small value in sample No. 28. Therefore, it is determined thataddition of at least 1 ppm of all of P, Cr and B to the electrodematerial is preferred. The deterioration rate was not suppressed to asmall value in relation to sample No. 23. Therefore it was confirmedthat the preferred content amount in the electrode material of P is nomore than 50 ppm, the preferred content amount in the electrode materialof Cr is no more than 500 ppm, and the preferred content amount in theelectrode material of B is no more than 50 ppm. A comparison of No. 24,25 and No. 26, 27 enables confirmation that the preferred content amountin the electrode material of P is no more than 30 ppm, the preferredcontent amount in the electrode material of Cr is no more than 100 ppm,and the preferred content amount in the electrode material of B is nomore than 10 ppm.

C-5 Summary

From the above results, the deterioration of the cathode can besuppressed by a relatively uniform configuration in the distribution ofatoms (small standard deviation).

It was confirmed that the content amount of additives (P, Cr and B)contained in the electrode material results in a small standarddeviation when 1 ppm≦P≦50 ppm, 1 ppm≦Cr≦500 ppm and 1 ppm≦B≦50 ppm.

From the point of view of a stable microstructure in a porous electrode,the content amount of additives (P, Cr and B) contained in the electrodematerial has been confirmed to be 1 ppm≦P≦30 ppm, 1 ppm≦Cr≦100 ppm and 1ppm≦B≦10 ppm. These results demonstrate an effect of strengthening ofthe backbone of a porous electrode by addition of a microscopic amountof the additives.

Wet assay (ICP analysis) was used to confirm that the macro compositionof each sample coincides with the well-formed composition of the rawmaterials.

The relationship between the atomic distribution and the deteriorationof the cathode is purported to be as follows.

Even when the overall composition of the powdered cathode materialcoincides with the well-formed composition, if the location(distribution) of respective elements is not uniform when themicro-portions are observed, the composition of those portions deviatesfrom the overall composition. Catalytic activity and conductivity is lowin such portions, and thereby a cathodic function during powergeneration operations is low. When operating as a fuel cell, currentflow tends to avoid such inactive portions, and thereby the currentdensity is increased in the periphery of such portions. As the result,the deterioration of such peripheral portions is accelerated.

Although the scattering of the atomic percentage was calculated in eachtable by use of a disintegrated product, since the spot diameter duringanalysis for a powdered material is smaller than the diameter of adisintegrated product, it was confirmed for all materials that there isno difference in relation to the atomic distribution configuration(scattering) from a disintegrated product.

What is claimed is:
 1. A cathode material for a solid oxide fuel cellcomprising: a complex oxide having a perovskite structure expressed bythe general formula ABO₃ with a standard deviation value of no more than10.3 for the atomic percentage of respective elements in the A sitemeasured using energy dispersive X-ray spectroscopy at 10 spots in asingle field.
 2. The cathode material for a solid oxide fuel cellaccording to claim 1, wherein the A site is selected from the groupincluding La and Sr.
 3. The cathode material for a solid oxide fuel cellaccording to claim 2, wherein the complex oxide is (La, Sr)(Co, Fe)O₃,(La, Sr)FeO₃, (La, Sr)CoO₃, or La(Ni, Fe)O₃.
 4. The cathode material fora solid oxide fuel cell according to claim 1, wherein the single fieldis a range observed by an electron microscope with a magnification of100 times to 5000 times.
 5. The cathode material for a solid oxide fuelcell according to claim 1, wherein a size of the respective 10 spots isno more than 1 micrometer.
 6. The cathode material for a solid oxidefuel cell according to claim 1, wherein the position of the 10 spots isselected from the single field on the basis of the concentration levelin 10 stages determined in response to a distribution of the atomicpercentage in the single field.
 7. The cathode material for a solidoxide fuel cell according to claim 6, wherein the concentration level ofthe 10 stages is set across the whole range of the distribution of theatomic percentage.
 8. A solid oxide fuel cell comprising a cathodecomprising: the cathode made of the cathode material according to claim1; an anode; and a solid electrolyte layer disposed between the cathodeand the anode.
 9. An interconnector material for a solid oxide fuel cellcomprising: a complex oxide having a perovskite structure expressed bythe general formula ABO₃ with a standard deviation value of no more than10.3 for the atomic percentage of respective elements in the A sitemeasured using energy dispersive X-ray spectroscopy at 10 spots in asingle field.
 10. A solid oxide fuel cell comprising: a porous supportbase plate including a gas conduit in an inner portion, the poroussupport base plate having electrical insulating properties; a powergeneration element including an anode, a solid electrolyte layer and acathode, the anode, the solid electrolyte layer and the cathode beingstacked in sequence on the porous support base plate; and aninterconnector made of the interconnector material according to claim 9,the interconnector connected to the power generation element.